1. Field of the Invention
This invention relates to a novel transition metal which is useful as a catalyst for polymerization of olefins.
2. Prior Art
It is well known to produce ethylene polymers or ethylene-xcex1-olefin copolymers with use of a catalyst composition comprising a zirconium compound, a transition metal compound such as titanocene and hafnocene compounds and an aluminoxane compound. This prior art catalyst is liable to form such a polymers which is of an extremely high catalytic activity and has a narrow molecular weight distribution and modal distribution. Such known transition metal compounds are represented by the formula (cyclopentadienyl)2MeRHal wherein R is a cyclopentadienyl or C1-C6 alkyl group or halogen, particularly chlorine, Me is a transition metal, particularly zirconium and Hal is halogen, particularly chlorine. Specific examples are bis(cyclopentadienyl)zirconiumdichloride (Cp2ZrCl2) and bis(cyclopentadienyl)zirconiummonomethylmonochloride Cp2Zr(CH3)Cl as disclosed in Japanese Laid-Open Patent Publication No. 58-19309. U.S. Pat. No. 4,404,344 also discloses a zirconium compound represented by the formula Cp2MeY2 wherein Me is zirconium, Y is hydrogen, a C1-C5 alkyl group, a C1-C5 metalalkyl group or a group of such as CH2AlR2, CH2CH2AlR2 and CH2CH(AlR2)2 of which each R is a C1-C5 alkyl group or a C1-C5 metalloalkyl group.
Moreover, another compounds are well known from Japanese Patent Publication No. 7-37488 disclosing (C5Rxe2x80x2m)pRxe2x80x3s(C5Rxe2x80x2m)MeQ3xe2x88x92p and Rxe2x80x3s(C5Rxe2x80x2m)2MeQxe2x80x2 wherein Me is zirconium or hafnium, each (C5Rxe2x80x2m) is a cyclopentadienyl group or a substituted cyclopentadienyl group, Rxe2x80x2 each may be the same or different and are one member selected from the group consisting of hydrogen and C1-C20 alkyl, alkenyl, aryl, alkylaryl and arylalkyl groups of which two adjacent members may form 4- through 6-membered condensed rings, Rxe2x80x3 is a C1-C4 alkylene group, germanium, silicone, a phosphino group or an amino group which crosslink two rings (C5Rxe2x80x2m), Q each may be the same or different and are a C1-C20 aryl, alkyl, alkenyl, alkylaryl or arylalkyl group or halogen, Qxe2x80x2 is a C1-C20 alkylidene, s=0 or 1, p=1 and, m=4 when s=1 and m=5 when s=0, and at least one of Rxe2x80x2 is a hydrocarbon group if m=5.
In recent years, there have been arising various demands for polyolefins in terms of physical properties and characteristics, such demands being directed to the production of polyolefins which are somewhat widened in molecular weight distribution or increased in molecular weight or which are completely free of halogen. It has been found that polyolefins tend to be effectively varied in properties and behaviors such as activity during polymerization depending on the type of a transition metal compound used therefor. Nowadays, a strong demand has been arising for a clean polyolefin free of halogen in view of problems in environment and hygienic.
An object of the present invention is to provide a novel transition metal compound which is stable in nature and eligible for use of the components of a polymerization catalyst for olefins.
The novel transition metal compound according to the invention is represented by the formula 
wherein M1 is an element of Group IVB in the Periodic Table, M2 is an element of Group IIIA in the Periodic Table, R1 and R2 each are a cyclopentadienyl group, a substituted cyclopentadienyl group, an indenyl group or a substituted indenyl group and may be bonded to each other through a C1-C18 hydrocarbon group and/or silylene group, R3 and R4 each are a hydrogen atom or a C1-C18 hydrocarbon group, R5 and R6 each are a hydrogen atom or a C1-C18 hydrocarbon group and R7 and R8 each are a hydrogen atom or a C1-C18 hydrocarbon group and may be bonded to each other to form one or more cyclic hydrocarbon group.
A typical example of the compound of the above formula (I) is represented by the formula 
wherein M1 is an element of Group IVB in the Periodic Table, M2 is an element of Group IIIA in the Periodic Table, R1 and R2 each are a cyclopentadienyl group, a substituted cyclopentadienyl group, an indenyl group or a substituted indenyl group and may be bonded to each other through a C1-C18 hydrocarbon group and/or silylene group, R3 and R4 each are a hydrogen atom or a C1-C18 hydrocarbon group, R5, R6, R9, R10, R11, R12, R13 and R14 each are a hydrogen atom or a C1-C18 hydrocarbon group and may be bonded to each other through a hydrocarbon group to form a cyclic hydrocarbon group.
The present invention provides a novel transition metal compound which is capable of becoming a catalyst component exhibiting an excellent catalytic activity when applied to polymerization of olefins. This novel transition metal compound can be synthesized without using a halogen-containing substance as a starting material and is a novel transition metal complex having a 5-membered ring formed by a transition metal compound of Group IVB, two carbons, a metal of Group III and hydrogen and the existence of such a transition metal complex has not ever been known. Furthermore, it has not been known to use this transition metal complex as a component of a catalyst for polymerization of olefins.
The novel transition metal compound of the invention is represented by the above-mentioned formula (I) and one of the features of this compound is exemplified by the metallacycle (5-membered ring) formed through the bond of carbon, carbon, M2 (an element of Group IIIA in the Periodic Table) and hydrogen to M1 (an element of Group IVB in the Periodic Table).
It is well known that a zirconocenemonoalkylmonohydride compound of which hydrogen and alkyl are bonded to zirconium forms a divalent zirconocene by reductive elimination reaction caused by the coupling of hydrogen and the hydrocarbon, as reported in xe2x80x9cOrganozirconium Compounds in Organic Synthesisxe2x80x9d written by E. Negishi, T. Takahashi in SYNTHESIS, 1-19, January 1988. Such a zirconocenemonoalkylmonohydride compound is susceptible to the reductive elimination reaction and thus is difficult to stabilize whereas the novel transition metal compound of the invention can suppress the occurrence of the reductive elimination by the formation of a metallacycle (five-membered ring).
The inventive compound is characterized by its stereostructure which is stabilized due to the formation of metaracycle (five-membered ring) containing hydrogen. The five-membered ring of cyclopentadienyl groups or indenyl groups can rotate and thus if two identical ligands are bonded thereto they can not be distinguished. As to Cp2ZrCl2 (Formula A below), it is reported in J. Organomet. Chem., 1964, 2,329 that the 10 hydrogen atoms (H1 of Formula A) bonding to the cyclopentadienyl group are classified of one single kind by 1H-NMR. As to Cp2Zr(Cl)CH2SiMe3 (Formula B below), it is reported in J. Chem. Soc. Dalton Trans., 1973, 445 that the 10 hydrogen atoms (H2 of Formula B below) bonding to the cyclopentadienyl group are likewise classified of one single kind by 1H-NMR. Furthermore, as to Ind2ZrCl2 (Formula C below), Bull. Soc. Chim. Fr., 1966, 3548 describes that the 6 hydrogen atoms (H3, H4 of Formula C) bonding to the 5-membered rings of the indenyl group are observed of two types by 1H-NMR. 
Whereas, as proved in Examples 1 and 2 hereinafter described, 1H-NMR analysis of the novel compounds as represented by Formulae D and E above, of the invention reveals that the 6 hydrogen atoms in total (H5, H6, H7, H8, H9 and H10 of Formula D and H11, H12, H13, H14, H15 and H16 of Formula E) are observed individually. 1H-NMR data of Examples 1 indicates that these hydrogens are present at a peak of 5.8 ppm, 5.5 ppm, 5.4 ppm, 5.1 ppm, 4.6 ppm, and 4.3 ppm, while 1H-NMR data of Examples 2 indicates that these hydrogens are present at a peak of 5.6 ppm, 5.4 ppm, 5.3 ppm, 5.3 ppm, 4.7 ppm and 4.4 ppm.
By these facts meant is that all of these 6 hydrogens are distinguished by the time scale of NMR and the rotation of the indenyl group is restrained. These facts has been confirmed by X-ray diffraction.
The features of the novel transition metal compound according to the invention are summarized as follows:
1. M1 of an element of Group IVB in the Periodic Table bonding through hydrogen to M2 of an element of Group IIIA in the Periodic Table
2. The stabilized stereostructure of the compound by the formation of metallacycle
3. No use of halogen in the process of synthesizing